It is generally known to identify compression wood, blue stain, and pitch in a wood sample. With respect to detecting compression wood, known methods would include optical and scanning electron microscopy to identify compression wood areas. In normal wood, the S2 layer (the thickest cell wall layer comprised of ordered microfibrils nearly parallel to the long axis of the cell) is continuous and characterized by low microfibril angles. In compression wood the S2 layer is fractured and is characterized by high microfibril angles. Microscopy methods have the disadvantage that they cannot be applied in real time, in an industrial setting with lumber moving at planar speeds (up to 2500 fpm). The other primary method used to identify compression wood consists of transmission imaging of thin cross sections of boards. In this method, thin cross sections are imaged in transmission mode either in a scanner or photographic setup. Areas of compression wood appear as relatively opaque areas. The severity of compression wood can be estimated by mapping the variation in opacity in these areas. More severe compression wood transmits less light than less severe areas. The thin section transmission method, however, is also not appropriate for a real-time industrial application for obvious reasons. In addition, methods for detection of blue stain and pitch have demonstrated shortcomings.
Accordingly, a need exists for methods for more efficient detection of compression wood, blue stain, or pitch in lumber.